GETTYSBURG, S.D. (AP) — South Dakota’s salmon population needs human help to survive.
Salmon that swim throughout Lake Oahe aren’t native to the state, and with the muddy bottoms of the Missouri River and its feeder creeks, they are not able to spawn naturally. They need streams with gravel and cobblestone bottoms to spawn naturally.
In their native environment, salmon swim upstream where the female releases her eggs into a “red” she dug from the gravel streambed. Males swim nearby and release their milt, consisting of sperm and other fluids, which fertilizes the eggs. Both parents die after spawning, and those eggs sit, covered with gravel, until they hatch in the spring.
So, in South Dakota, fisheries personnel with the state’s Game, Fish and Parks Department manually spawn the fish at Whitlock’s Spawning Station located on Lake Oahe, west of Gettysburg.
In the late 1970s the state first stocked salmon into Lake Oahe with fish from the Great Lakes and the West Coast. In 1984 the spawning station was built, and in 1988 the state stocked its last Great Lake salmon, said Mike Barnes, the manager of McNenny State Fish Hatchery.
Since that time the salmon population has been maintained by spawning the salmon at Lake Oahe, occasionally from eggs received from North Dakota.
On Oct. 14, the fisheries personnel spawned about 60 salmon.
In the fall, the fish naturally want to swim upstream to spawn. The spawning station has a fish ladder that they swim up and into rectangular holding structures. Crews also electrofish bays to ensure more fish are available to spawn.
They are then sorted manually by gender.
If they are ready to spawn they are moved into spawning stations. The males are usually all ready to spawn in the fall. The timing depends on the females.
To see if the females are ready to spawn fisheries personnel simply pick up the fish. If eggs flow freely from their vents, a small opening on their belly, they are ready. If eggs do not fall, the female fish is placed back in the holding area where she will later release the eggs into her body cavity when she is ready to spawn.
This year the fish are much larger than normal, and as a result there are more eggs per female — 3,500 to 4,000 eggs per female. That’s well above average. Typically they average 2,400 to 2,500 eggs per female.
The reason for the larger fish this year may be two fold. All the fish that were spawned were stocked after the Missouri River flooding of 2011. Following the flood recruitment numbers were poor, but those that survived enjoyed good baitfish numbers, said Robert Hanten, a fisheries biologist with the GF&P.
When it is deemed that the fish are ready to spawn they are euthanized in a bath of carbon dioxide.
The males are picked up and their abdomens are squeezed. Milt, or sperm, will flow from their bodies. For females, a needle is inserted into their abdomens and compressed air is pumped in which forces the eggs out into a pan.
A small amount of milt is added to the eggs and then water is added.
The milt is inactive until it comes into contact with water.
“Once water is added to the mix, that’s when fertilization takes place,” Hanten told the Black Hills Pioneer ( ).
The fish sperm has about 30 seconds to fertilize the eggs. The eggs are then rinsed a few times and are allowed to sit undisturbed in coolers.
“Immediately after fertilization there are some changes to the eggs,” Barnes said. “There are some membranes inside the external membrane. Those membranes separate and water is infused into the egg at a rapid rate. It’s called water hardening and that provides a protective cushion. But when the membranes are separated, the eggs are really fragile, so they are put in water and allowed to set for an hour.”
Water infuses into the eggs that swell in size. Only then can they be safely be transported to the hatchery.
Eggs are kept in an incubator at the hatchery and will sit undisturbed for about a month until the eggs develop to a point where you can see their eye pigments. They can then be safely handled. The eggs are placed in a sorting machine that removes all the white eggs, which are no longer viable and a source for bacteria.
The flesh colored viable eggs go back into the jars for another three weeks until they hatch. The hatchlings feed off their eggs for another month and will then be fed artificial feed afterward.
By April, the fish will be about 3 to 4 inches long and will be trucked sometime between then and June back to Lake Oahe where they will swim freely once again.
Barnes said some fish will be kept until November when they are 9 to 10 inches long.
The following fall the spawning cycle begins again. Some males stocked from the year before will arrive at the spawning station.
“They aren’t large but they are mature,” Barnes said.
Typically the males spawn between the age of 2 and 4 years and the females spawn at 3 to 4 years old. A long-term average of 800 to 850 fish is spawned each year. Hanten said he hopes to have half that number this year since the population is still recovering from the flood.
Fisheries crew remove parts of the salmon’s kidneys to test for diseases, and on some fish, their heads are removed so a small metallic tag can be retrieved. Hanten encouraged anglers who catch salmon, to turn their heads into the GF&P or local bait shops so the tags can be retrieved. The salmon missing their adipose fin are the tagged fish.
Anglers who turn in the tags receive a letter telling them about the fish they caught and are entered into a drawing to win $100.
In turn, biologists use information from the tags to determine when and where each salmon was stocked. This allows them to better identify stocking location that could lead to better angling opportunities and return to the salmon spawning station.
Information from: Black Hills Pioneer,